1. Field of the Invention
The present invention relates to a jacketed antenna, and more particularly to a mobile telephone antenna for motor vehicles that can be attached and detached from motor vehicles by rotation of the antenna so that the jacket surrounding the antenna does not slip relative to encased interior antenna electrically conductive parts when the jacket is rotated for attachment and detachment of the antenna.
2. Description of the Related Technology
Antennas, especially mobile telephone antennas for motor vehicles, are known. These antennas often have a base body from which an electromagnetic wave receiving portion extends, such as an antenna coil or an antenna rod. Further such base bodies also are conductive and can be made of metal with a corresponding contact area for mating onto a motor vehicle by, for example, being threaded onto the motor vehicle body. Often a large portion of the base body, except for the contact area, and at least some part of the antenna receiving portion, are surrounded with an electrically nonconductive jacket to protect the covered metal parts from atmospheric caused corrosion and also to achieve an overall more pleasant appearance for the antenna structure. This jacket design for antennas makes it possible for the antenna conveniently to be removed from a motor vehicle, for example prior to having the motor vehicle moved through a car wash. It also is important, though, that when a detachable antenna is mounted on vehicle that there must be both good mechanical and electrical connections between the antenna and the vehicle to ensure structural stability and electrical transmission in order to provide effective antenna operation. In the case of antenna and vehicle screw connections via which an antenna is attached to a vehicle by a screw type connection, it is important that these screw type connections be maintained tight to prevent antennas from falling off of vehicles and from failing to maintain continuous electrical contact between the antenna and the motor vehicle. Antenna designs based on metal components being encased inside nonconductive jackets run the risk that such antennas will not be screwed tight to motor vehicle bodies because of the very real possibility of relative motion between the antenna metal inner components and the outside jackets which are all that can be gripped to rotate the antenna structure. Such rotary motion imported from a gripped jacket causes a force which acts on at least one flank of the antenna base body. This force acts on an oblique surface of the antenna base body (see FIG. 4A). Therefore, the prior art nonconductive jacket can slip around encased antenna conductive parts. This situation means that the prior art antenna may not be securely joined to the installation site. These insecure installation problems arise especially when the prior art antenna base body and the receiving portion have generally round exterior cross sections, which often are a design selection made for economic reasons to facilitate economical series production of antennas.